An underdog GOP candidate challenging Florida Sen. Marco Rubio's bid for re-election lashed out at the incumbent's no-show in Cleveland, where Donald Trump became the party's standard-bearer Tuesday night.

"I'm here to back up Donald Trump all the way to the White House, unlike Mr. Rubio, whose afraid to take a stance," Carlos Beruff declared, the Sarasota Herald-Tribune reports.

"He's melba toast on him," Beruff said of Rubio's lukewarm support for Trump, whom the candidate hopes to make a litmus test in the campaign, the Herald-Tribune reports.

"Rubio can't hold Trump's water," he added.

According to the Herald-Tribune, the tough-talking homebuilder is spending big to advance his campaign, though polls show Rubio with a lead over him — and last week devoted $1 million to statewide television ads.

On Tuesday, Beruff said he shelled out "another million yesterday" and plans to lay out "another million next week."